Experiments are underway to characterize a number of markers for rabbit lymphoid cells. the major approach used is to clone the genes encoding cell surface molecules known to be involved in identification of functionally distinct cell subsets. These will be valuable in identifying distinct cell populations and in evaluating the expression of the genes in lymphoid tissues. These genes will be expressed for the production of monoclonal antibodies to the cell surface markers or as soluble forms of the cell bound products that may be used for inhibition studies. The gene for rabbit CD4 has been cloned and sequenced. It is being expressed as a membrane form on the cell surface as well as soluble form. The product of both expression systems can be used to determine the efficiency of HIV-1 binding to cells. The gene for rabbit CD8 is being cloned from a cDNA library. CD4 and CD8 identify important subpopulations of T cells. The genes for IL2, IL2R alpha and those for the gamma and delta chains of the T cell receptor are also under investigation. The molecular probes and other reagents derived from the genes can be used for monitoring these markers in the human retrovirus disease models being developed in the rabbi